The present invention, in some embodiments thereof, relates to a composition comprising at least two active agents for the treatment of diseases and, more particularly, but not exclusively, to neurodegenerative diseases.
Amyotrophic Lateral Sclerosis (ALS) is a fatal, rapidly progressive, neurodegenerative disease characterized by loss of motor neurons in the motor cortex, brainstem and spinal cord. This motor neuron degeneration results in weakness, muscle atrophy, fasciculations and paralysis, a process culminating in death due to respiratory failure within 2-5 years of clinical onset (Charles and Swash, 2001; Oliveira and Pereira, 2009). Despite extensive efforts the underlying cause of ALS and the path of neurodegeneration remain elusive. This led to the proposal of numerous hypotheses including; reduced neurotrophic factor secretion, mitochondrial dysfunction, toxic intracellular aggregations and axonal impairment due to neurofilament accumulation (Benkler et al., 2010; Lev et al., 2009; Offen et al., 2009; Rothstein, 2009; Van Damme et al., 2005; Xiao et al., 2006). One of the currently most prominent pathophysiological hypotheses explaining ALS progression involves glutamate excitotoxicity and oxidative stress (Bogaert et al, 2010; Rothstein, 2009; Van Damme et al. 2005).
Preventing or slowing motor neuron degeneration and death in ALS are critical goals of future therapies.
The selective motor neuron death which occurs in ALS led researchers to explore cell autonomous mechanisms. However, studies performed in the SOD1 fALS mouse model suggest that non-neuronal cells such as astrocytes and microglia might be at play (Ilieva et al., 2009; Yamanaka et al., 2008; Di Giorgio et al., 2007; Beers et al., 2006; Boillée et al., 2006; Clement et al., 2003).
Astrocytes play a crucial role in the function and survival of motor neurons through numerous mechanisms, among them are secretion of neurotrophic factors, maintenance of synaptic glutamate homeostasis and modulation of the neuronal susceptibility to glutamate excitotoxicity. Increasing evidence indicate astrocytic dysfunction in all three mechanisms may well be instrumental in the pathogenesis of ALS (Van Den Bosch and Robberecht, 2008; Staats and Van Den Bosch, 2009). Under physiological conditions astrocytes are activated by stress signals from their environment. Altered response to those stress signals may prove harmful to the wellbeing of the CNS. It was found that astrocytes derived from the SOD1 G93A ALS mouse model exhibit a reduced glutamatergic and trophic response to specific activations compared to their wild-type counterparts. Wild-type astrocytes exhibited a robust response when activated with lipopolysaccharide (LPS), G5 or treated with ceftriaxone in many parameters evaluated.
These parameters include increased expression of GLT-1 and GLAST the two major astrocytic glutamate transporters, accompanied by a marked increase in the astrocytic glutamate clearance and up-regulation of neurotrophic factor expression. However, not only do un-treated SOD1 G93A astrocytes take up glutamate less efficiently, but in response to activation they show no further increase in any of the glutamatergic parameters evaluated. Furthermore, activation of wild-type astrocytes, but not SOD1 G93A astrocytes, improved their ability to protect the motor neuron cell line NSC-34 from glutamate induced excitotoxicity. Such data indicates that altered astrocyte activation may well be pivotal to the pathogenesis of ALS.
It has been proposed that the reduced glutamatergic and trophic response of astrocytes to activation in ALS, may, over time, lead to disruption of glutamate homeostasis and accumulative CNS damage, thus facilitating motor neuron degeneration.
Glutamate is the main excitatory amino acid (a.a) neurotransmitter in the human central nervous system (CNS). It plays a major role in learning, development, synaptic plasticity, cognitive functions and behavior (Danbolt, 2001; Maragakis and Rothstein, 2001; Mattson, 2008; Molz et al., 2008). However, overstimulation of glutamate receptors leads to neuronal degeneration, a process commonly referred to as glutamate excitotoxicity (Attwell, 2000; Bogaert et al, 2010; Brown, 2000; Danbolt, 2001; de Hemptinne et al. 2004; Foran and Trotti, 2009; Lee et al., 2007; Mattson, 2008; Maragakis and Rothstein, 2001; Sheldon and Robinson, 2007; Sonnewald et al., 2002; Van Damme et al., 2005).
Abnormal glutamate metabolism accompanied by selective loss of the astroglial glutamate transporter-1 GLT-1 (and its human counterpart EAAT2) were observed in sporadic and familial ALS patients as well as in mutant SOD1 animal models (Rothstein et al., 1992; Rothstein et al., 1995; Bendotti et al., 2001). Furthermore, both in vitro and in vivo experiments demonstrate that selective loss of GLT-1 can lead to motor neuron degeneration (Rothstein et al., 1996).
Glutamate excitotoxicity can lead to secondary oxidative stress which in turn causes severe motor neuron injury and death (Lynch and Guttmann, 2002). NRF2 is a transcription factor which activates genes containing the antioxidant response element (ARE), thus constituting a major node in the cellular anti-oxidative response (Hybertson et al., 2011; Vargas and Johnson, 2009). It has been previously shown that activation of NRF2 specifically in astrocytes protects neurons from a variety of in vitro insults as well as conveys protection in an ALS mouse model (Calkins et al., 2010; Kraft et al., 2004; Shih et al., 2003; Vargas et al., 2006, 2008 and 2009).
Riluzole has been approved for the treatment of ALS. Its mechanism of action may be partly due the prevention of stimulation of glutamate receptors. It may be provided alone or together with antioxidants such as vitamin C or E.
U.S. Application No. 20090304661 teaches administration of glutamate modifying enzymes and stress hormone modulating agents for the treatment of neurodegenerative diseases.
U.S. Application No. 20110250300 teaches administration of agents that cause the upregulation of Nrf2 for the treatment of neurodegenerative diseases.
Rothstein, J. D., Martin, L. J., and Kuncl, R. W. (1992). N. Engl. J. Med. 326, 1464-1468; Rothstein, J. D., Jin, L., Dykes-Hoberg, M., and Kuncl, R. W. (1993). Proc. Natl. Acad. Sci. USA 90, 6591-6595; Rothstein, J. D., Martin, L., Levey, A. I., Dykes-Hoberg, M., Jin, L., Wu, D., Nash, N., and Kuncl, R. W. (1994) Neuron 13, 713-725 teach that EAAT2 is dysfunctional in ALS patients.